Bob - if you're referring to the effect known as the 'sunset glow', then this wouldn't be seen on clear glass, and occurs only on translucent pieces and around the edges of opaque milk glass - presumably only on those pieces that contain phosphates, and is seen when viewing the glass under transmitted light (i.e. light viewed after it has passed through the glass - as opposed to reflected light). The reason being, presumably, is that the additives (to the batch) that give rise to these reddish tones prevent the glass from remaining clear.
According to the books, prior to c. 1930 this effect was created by powdered calcined animal bones, but on later pieces the effect was achieved in a more controlled way by addition of the chemical phosphates alumina and fluorine.
As a decorative effect (within glass) it seems to have had a long history.
I'm sure I've seen these 'hens on nest' in clear glass, but I'd take a guess that there are a lot more in opaque white glass, with a lesser quantity being coloured. Sowerby did a frosted chic butter dish apparently, but no sunset glow it seems. I believe that the expression 'milk glass' - when these things appear as opaque white glass - was originally a piece of terminology from the States, but Belknap's book does include a few pieces in colours other than white. Unfortunately, he makes no mention of the make-up of the glass, or for that matter any reference to a sunset glow.
I've not been aware of seeing an example from China, but it seems from what you're saying that the modern examples are simply opaque white glass minus the phosphates, thus missing the sunset glow?
In the past there have been mammoth discussions on the GMB, in an attempt to define peoples' views on the differences between opal, opalescent, opaline and opaque white glass - I should think you could float the Bismark with the ink we have used
P.S. Chris - for my money, The Decanter Book is miles out ahead of the Hen on Nest book (with apologies to Shirley Smith)

P.P.S. my humble suggestion would be to avoid the word 'opaline' for pieces such as this i.e. plain white opaque material. The word opaline is a description that seems to have been used specifically to describe the pastel coloured partly translucent glass - mainly coloured with metallic oxides (dark blue and even black) - with an appearance less dense (and more delicate) than ordinary opaque white glass.
Often French (Baccarat), but also from Bohemia and Murano.
It's rare that I'd agree with a modern States description

, but in this instance I'm happy with 'milk glass', failing which simply opaque white glass.